Freight containers for use in the intermodal transportation of goods regularly comprise eight corner fittings, one at each corner, the four lower serving to secure the container to locking members such as pins or twistlocks provided on vehicle platforms, and the four upper being adapted for engagement by hoisting gear such as crane hooks or spreaders. ISO containers having standardized corner fittings are predominantly manufactured in widths of 8 ft. (2438 mm) and in lengths of 10 ft. (2991 mm), 20 ft. (6058 mm), 30 ft. (9125 mm), and 40 ft. (12192 mm), and the openings provided in the corner fittings for engaging locking members are spaced center-to-center by 2259 mm in the lateral direction and 2787 mm, or 5853 mm, or 8918 mm, or 11985 mm, respectively, in the longitudinal direction.
FIG. 1 schematically represents a plan view of the loading platform of a typical railway waggon having an overall length (without buffers) of approx. 60 ft. (about 18.3 m) for selectively receiving such freight containers. As can be seen from FIG. 1, a total of twenty-eight locking pins are provided, which are usually hinged to the platform to be individually turned down. Twenty-four of these pins are indicated at A and our are indicated at B. Up to six 10-ft. containers, or three 20-ft. containers, or two 30-ft. containers, or one 40-ft. container and one 20-ft. container etc. may be optionally secured to locking members situated at A. The pins provided at locations B serve to secure a container (or more generally: a unit load) of a non-ISO length of 35 ft. (about 10675 mm). All locking members are disposed on two axes extending in the travelling direction of the waggon at the standard spacing of 2259 mm. (It should be noted that in FIG. 1 the legends such as "10-ft cont." refer to the lengths of containers that may be secured to locking members disposed at the respective positions, whereas the actual distance between these locking members is not 10 ft etc. but shorter as explained above.)
Similar conditions exist on loading platforms of container road vehicles, with twistlocks being provided there instead of pins (that are sufficient in railway waggons).
Due to the above dimensions, there are a total of five locations on either side of the platform where pairs of locking members arranged at A are spaced by about 280 mm, as shown in FIG. 1.
Small and medium-size tank containers and unit loads have been developed for transporting small or medium quantities of flowable goods, and these containers are dimensioned so that two, three or more of them may be modularly arranged on an ISO flat ("Platform Based Container" according to ISO 1496-6), with the flat itself comprising lower corner fittings for securing to locking members arranged at the distances mentioned above. Such small or medium-sized containers typically have a width of 2200 mm and lengths of 1900 mm up to 2900 mm.
In order to handle such smaller containers of non-standard dimensions and secure them at the locking members provided on common loading platforms, U.S. Pat. No. 4,682,923 proposes latch plates disposed in two lower frame members that extend parallel to the travelling direction during transport, which latch plates have a portion that may be extracted from a corner opening and fixed at a respective one of the locking members. This arrangement permits securing the container at a transverse axis substantially coinciding with the lower front or rear container edge in the travelling direction. This type of locking involves a certain risk of the container to turn over as a result of vertical or horizontal accelerations as occur in road transport in particular.
A way to reduce this risk of tilting is known from U.S. Pat. No. 4,768,906, where latch plates are no longer provided in the region of the lower container corners, but engage openings provided in intermediate regions of the lower frame members. Again, the container is locked with respect to one transverse axis only, so that all acceleration forces occurring due to shunting bumps or braking must be taken up by a total of two locking members and two latch plates.